AST 105 Chapter 11 (6)

Why does the Sun shine?

As the Sun was forming, gravitational contraction increased the Sun's temperature until the core become hot enough for nuclear fusion, which ever since has generated the heat that makes the Sun shine.

How can we measure the strength of magnetic fields on the Sun?

By looking for the splitting of spectral lines in the Sun's spectrum.

Every second, the Sun converts about 600 million tons of hydrogen into 596 million tons of helium. The remaining 4 million tons of mass is _________.

Converted to an amount of energy equal to 4 million tons times the speed of light squared.

The Sun layers in order:

Core, Radiation Zone, Convection Zone, Photosphere, Chromosphere, Corona.

What happens to energy in the Sun's 'convection zone'?

Energy is transported outward by the rising of hot plasma and sinking of cooler plasma.

The intricate patterns visible in an X-ray image of the Sun generally show _______.

Extremely hot plasma flowing along magnetic field lines.

The fundamental nuclear reaction occurring in the core of the Sun is __________.

Nuclear fusion of hydrogen into helium.

According to modern science, approximately how old is the Sun?

4 1/2 billion years old.

The overall result of the proton-proton chain is _______.

4 H becomes 1 He + energy.

The basic fusion reaction through which the Sun produces energy is _________.

4 hydrogen nuclei fuse to make 1 helium nucleus.

The Sun's average surface (photosphere) temperature is about ___________.

5,800 K.

What is the Sun's approximate composition (by mass)?

70% hydrogen, 28% helium, 2% other elements.

The light radiated from the Sun's surface reaches Earth in about 8 minutes, but the energy of that light was released by fusion in the solar core about __________.

A few hundred thousand years ago.

How is the sunspot cycle directly relevant to us here on Earth?

Coronal mass ejections and other activity associated with the sunspot cycle can disrupt radio communications and knock out sensitive electronic equipment.

Satellites in low-Earth orbits are more likely to crash to Earth when the sunspot cycle is near solar maximum because _________.

Earth's upper atmosphere tends to expand during solar maximum, exerting drag on satellites in low orbits.

If the Sun suddenly stopped emitting neutrinos, what might we infer (after checking that our neutrino detectors were still operational)?

Fusion reactions in the Sun have ceased within the past few minutes.

What two items are in balance in what we call 'gravitational equilibrium'?

Gas pressure and Gravity.

What two physical processes balance each other to create the condition known as gravitational equilibrium in stars?

Gravitational force and outward pressure.

In the late 1800s, Kelvin and Helmholtz suggested that the Sun stayed hot due to 'gravitational contraction'. What was the major drawback to this idea?

It predicted that the Sun could shine for about 25 million years, but geologists had already found that Earth is much older than this.

When was gravitational contraction an important energy generation mechanism for the sun?

It was important when the Sun was forming from a shrinking interstellar cloud of gas.

Why does the Sun emit most of its energy in the form of visible light?

Like all objects, the Sun emits thermal radiation with a spectrum that depends on its temperature, and the Sun's surface temperature is just right for emitting mostly visible light.

All the phenomena of solar activity — including sunspots, flares, coronal mass ejections, and the sunspot cycle — are tied to changes in the Sun's __________.

Magnetic Field.

A salesperson attempts to convince you to purchase a "solar neutrino" shield to protect you and your family. Why do you turn down this excellent offer?

Neutrinos rarely, if ever, interact with other matter.

What best explains why nuclear fusion requires bringing nuclei extremely close together?

Nuclei normally repel because they are all positively charged and can be made to stick only when brought close enough for the strong force to take hold.

The Sun's visible surface (that is, the surface we can see with our eyes) is called the __________.

Photosphere.

What correctly compares the Sun's energy-generation process to the energy-generation process in human built nuclear power plants?

The Sun generates energy by fusing small nuclei into larger ones, while our power plants generate energy by the fission (splitting) of large nuclei.

How does the Sun's mass compare to Earth's mass?

The Sun's mass is about 300,000 times the mass of the Earth.

We can essentially rule out the Sun as a cause of global warming over the past few decades because __________.

The amount of incoming sunlight has decreased while Earth's average temperature has increased.

How can we best observe the Sun's chromosphere and corona?

The chromosphere is best observed with ultraviolet telescopes and the corona is best observed with X-ray telescopes.

If the Sun's core suddenly shrank a little bit, what would happen in the Sun?

The core would heat up, fusion rates would increase, the core would re-expand.

The energy that is released in the hydrogen fusion reaction comes from ___________.

The difference in mass between the four hydrogen nuclei and the single resulting helium nucleus.

What two items are in balance in what we call 'energy balance'?

The energy released into space, and the energy produced by fusion.

Energy balance in the Sun refers to a balance between _________.

The rate at which fusion generates energy in the Sun's core and the rate at which the Sun's surface radiates energy into space.

Which of the following is NOT a characteristic of the 11-year sunspot cycle?

The sunspot cycle is very steady, so that each 11-year cycle is nearly identical to every other 11-year cycle.

What do we mean when we say that the Sun is in gravitational equilibrium?

There is a balance within the Sun between the outward push of pressure and the inward pull of gravity.

Why do sunspots appear dark in pictures of the Sun?

They are actually fairly bright, but appear dark against the even brighter background of the surrounding photosphere.

What do sunspots, solar prominences, and solar flares all have in common?

They are all strongly influenced by magnetic fields on the Sun.

Why are neutrinos so difficult to detect?

They have a tendency to pass through just about any material without any interactions.

To estimate the central temperature of the Sun, scientists __________.

Use computer models to predict interior conditions.

What are the appropriate units for the Sun's luminosity?

Watts.

The Sun's surface seethes and churns with a bubbling pattern. Why?

We are seeing hot gas rising and cool gas falling due to the convection that occurs beneath the surface.

What is NOT a way by which we can study the inside of the Sun?

We can send a space probe into the Sun's photosphere. -It is WAY too hot to do this.

What correctly describes how the process of 'gravitational contraction' can make a star hot?

When a star contracts in size, gravitational potential energy is converted to thermal energy.

What is the solar wind?

a stream of charged particles flowing outward from the surface of the Sun.

When we say that the Sun is a ball of "plasma", we mean that __________.

the Sun consists of gas in which many or most of the atoms are ionized (missing electrons).

The 'proton-proton chain' is ______________.

the specific set of nuclear reactions through which the Sun fuses hydrogen into helium.